Inductance



April 1941 J. E. JOHANSON 2,238,420

INDUCTANCE Filed May 21, 1938 Patented Apr. 15, 1941 INDUCTANCE John E. Johanson, Boonton, N. J assignor to Aircraft Radio Corporation, Boonton, N. J a corporation of New Jersey Application May 21, 1938, Serial No. 209,297

4 Claims.

This invention relates to inductances and particularly to adjustable inductances such as may be employed as antenna coils in radio equipment.

The simple method of tapping a coil of spaced turns of bare wire by a conductive member which is wedged between adjacent turns is undesirable in radio circuits due to losses arising from the short-circuiting of one turn of the winding. It has been proposed to avoid this short-circuiting by using a tapping member having conductive and non-conducting surfaces for wedging contact with adjacent turns of the coil, the tapping member being a spring-pressed plunger carried by a slide that is movable along a rod at the side of the coil. The proposed construction did avoid the short-circuiting of adjacent turns but the construction was expensive to manufacture and the mechanical design was such as to require some sacrifice of or compromise between desirable electrical and mechanical design features. For example, a high spring pressure on the plunger to insure good electrical contact engagements resulted in a high rate of wear and destructive forces when the tapping member was adjusted along the coil. High spring pressure also made it difficult to adjust the tap. The prior construction added materially to the effective diameter of the coil assembly, and the contact surfaces were not visible for inspection.

Objects of this invention are to provide tapped inductances of simple and inexpensive design, and which are characterized by self-cleaning tap members that afford good electrical contact engagements and may be readily adjusted manually. An object is to provide a tapped inductance having spaced turns of bare wire, and a tap member in the form of a disk slidable and rotatable upon a rod that is spring-pressed toward the inductance. A further object is to provide a tapped inductance of the type stated in which the tap member takes the form of a disk or button having conductive and insulating surfaces at its opposite faces.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Figs. 1 and 2 are side elevations, from opposite sides, of an embodiment of the invention;

Fig. 3 is an end View of the same; and

Fig. 4 is a fragmentary view, with parts in section, of the tap member, its supporting rod, and two turns of the coil winding.

In the drawing, the reference numeral l identifies the base of a ribbed coil form 2 of known type in which the ribs have grooves 3 for the reception of spaced turns of a coil 4 of bare wire. The illustrated coil is of the plug-in type and the base I has apertures in which conductive sleeves or plugs 5 are secured for cooperation with resilient jack or terminal members. The inner and outer ends of the coil are connected to soldering lugs 6, I, respectively, that are secured to the bottom of base I by two of the sleeves 5, and a lead 8 extends from an intermediate point on the coil to a soldering lug 9 that is secured to the upper face of the base I by another sleeve 5.

The electrical and mechanical design, so far as described above, may be varied to meet particular requirements for any given inductance and circuit arrangement. This invention contemplates an adjustable tap connection to a desired intermediate point on the coil winding 4.

The ends of a pair of arcuate leaf springs I0 are secured by bolts II to one of the ribs of the coil form 2 and the other ends of these springs overlie the next adjacent rib and support a rod I2 on which the contact assembly is slidably and rotatably mounted. The contact assembly takes the form of a disk or button and comprises a domed contact head I3 on one end of a sleeve I4, and an insulating washer I5 on and secured to the sleeve by spinning over the end of the sleeve upon a washer I6 which bears against the insulating washer. The contact head I3 and insulating washer I5 merge into each other at their outer surfaces and their outer edges are symmetrically rounded ofi to engage adjacent turns of the coil winding I.

The electrical circuit from the contact head I3 is through the sleeve I4, rod I2 and the inner spring II] to the lead I? that is soldered to a terminal lug I8 that is fixed to the base I by a sleeve or plug rivet 5.

The springs II] have such normal curvature that the rod I2 is urged radially towards the coil under a substantial pressure which insures good contact engagements between the rod I2 and sleeve I4, and between the contact head I3 and the coil wire 4. A relatively high spring pressure is permissible as the contact head may be easily moved from one turn to the next by first lifting the rod I2. The contact assembly is of relatively small diameter and there is no tendency towards binding when pressure is applied to move the contact assembly along the rod. The contact assembly may be grasped by its lateral edges, thus applying pressure substantially axial- 1y of the rod 2. The contact surfaces may be cleaned, when desired, by rotating the contact disk assembly without changing its position of adjustment on the coil, and the contact surfaces are visible for inspection. The space requirements for the adjustable contact assembly are small and add little or nothing to the overall diameter of the inductance.

It is to be understood that the mechanical design of the adjustable tap may be varied within Wide limits and that many variations fall within the spirit of my invention as set forth in the following claims.

I claim:

1. An adjustable tap inductance for use at radio frequencies, said inductance comprising a coil form, a coil of spaced turns of bare wire supported on said form, a conductive rod extending along said coil form, spring means fixed to said coil form for urging said rod radially towards said coil, a sleeve slidable and rotatable upon said rod, said sleeve having a domed contact head at one end thereof, a domed washer of insulating material on said sleeve and merging into said domed contact head, said domed 2.

head and washer being projected between and into contact with adjacent turns of said coil by said spring means, whereby said spring means must yield to permit a manual displacement of said sleeve for engagement of the domed contact head with another turn of the coil, and terminal means onv said coil form electrically connected to one of said spring means and to at least one end of said coil.

2. In an inductance for use at radio frequencies, a coil form having a plurality of grooved ribs, a coil of bare wire wound on said coil form and in the grooves of said ribs, a pair of arcuate spring members secured to opposite ends of one of said ribs and having outer ends overlying the next adjacent rib, a conductive rod secured to the outer ends of said spring members, and a tap member of disk formed slidably and rotatably supported on said rod, said tap member having a rounded outer edge portion for engaging adjacent turns of the coil, the edge P rtion comprising one face of conductive material and an opposite face of insulating material.

3. An adjustably tapped inductance for use at radio frequencies and of the type including a coil form carrying spaced turns of bare wire, a conductive rod extending along said coil form, spring means fixed to said coil form and yieldingly pressing said rod towards said coil form, and a tap member adjustable along said rod to engage said wire, characterized by the fact that said tap member is of disk form rotatable on and slidable along said rod, one face of said disk being of conductive and the other of insulating material.

4. An adjustably tapped inductance as claimed in claim 3, wherein said spring means comprises arcuate leaf springs at opposite ends of said coil form to press said rod towards the same, the opposite ends of said springs being secured respectively to said coil form and to said rod.

JOHN E. JOHANSON. 

